Amine alanes, complexes of tertiary amines with AlH.sub.3, are used in various reduction processes, in the preparation of aluminum, and in the production of silane. See, for example, Marlett, U.S. Pat. No. 4,474,473, issued Oct. 2, 1984; Brendel, U.S. Pat. No. 3,552,946, issued Jan. 5, 1971.
The production of amine alanes has been accomplished by several methods (see Nelson, Becker, and Kobetz, U.S. Pat. No. 3,651,064, issued Mar. 21, 1972, and references therein).
Dilts and Ashby, Inorg. Chem. 9(4), 855 (1970), in a study of complex metal hydrides in tertiary amine solvents, found that trimethylamine extracted alane from lithium aluminum hydride, LiAlH.sub.4, to produce an amine alane, AlH.sub.3.2N(CH.sub.3).sub.3, in a yield of 30% after one month. In diethyl ether solution the one-month yield was 98%. At 0.C in diethyl ether solution, the 24-hour yield was only 27%. In benzene, Li.sub.3 AlH.sub.6 was produced, but the amine-containing product was not characterized. Other amines effected no extraction of alane; the product of reacting LiAlH.sub.4 with other amines, if any, was an adduct of LiAlH.sub.4. The effective use of solutions of amine alane is complicated by the presence of soluble lithium in the amine complex, for example, a soluble amine adduct of LiAlH.sub.4.
Dilts and Ashby, in the same study, were unsuccessful in extracting alane from sodium aluminum tetrahydride by any amine.
Other workers (Peters, Can. J. Chem. 42, 1755 (1964); Ehrlich and Rice, Inorg. Chem. 5, 1284 (1966)) did not effect the extraction of AlH.sub.3 from LiAlH.sub.4 by any tertiary amine other than trimethylamine. Moreover, with this amine, either the yields were quite low or the reaction time was unfeasibly long. Also, of course, dealing with the gaseous amine reactant involves greater difficulty and inconvenience than with a liquid.
Lithium aluminum tetrahydride may be prepared as described by Finholt, Bond, and Schlesinger, J. Am. Chem. Soc. 69, 1199 (1947), by the reaction of LiH with AlCl3 in diethyl ether. It also may be produced, as taught by Ashby et al., Inorg. Chem. 2, 499 (1963), by the reaction of lithium hydride with aluminum and hydrogen in tetrahydrofuran or diglyme. A drawback to this method is the difficulty of removing all of the solvent from the product. Another route is the reaction of lithium chloride with sodium aluminum tetrahydride, as taught by Robinson (French Patent No. 1,245,361, 1960).
In one process for preparation of sodium aluminum tetrahydride, aluminum and hydrogen react with the hexahydride, Na.sub.3 AlH.sub.6, under pressure, as taught by Beaird and Kobetz, U.S. Pat. No. 3,355,262, issued Nov. 28, 1967.